One typical conventional cellular phone will be described below with reference to FIGS. 1(a) through 1(c) of the accompanying drawings. FIG. 1(a) is a front elevational view of the cellular phone, FIG. 1(b) a cross-sectional view of the cellular phone with an antenna assembly extended, and FIG. 1(c) a cross-sectional view of the cellular phone with the antenna assembly retracted in a case.
As shown in FIGS. 1(a) through 1(c), the conventional cellular phone comprises antenna assembly 1 including whip antenna 1a and helical antenna 1b, feeder 2, printed-circuit board 3, ground layer 3a, outer case 4, through hole 7, liquid-crystal screen 8, and keypad 9. The printed-circuit board supports thereon circuits and related components for transmitting and processing signals and electric power. However, these circuits and related components are omitted from illustration in FIGS. 1(a) through 1(c).
The cellular phone is basically constructed of antenna assembly 1 for radiating radio waves for communication with a base station, feeder 2 for supplying electric power to the antenna for radiating radio waves therefrom, and printed-circuit board 3 supporting thereon circuits and other components for generating and transmitting electric power. Usually, printed-circuit board 3 comprises a multilayer board having an inner layer (conductive layer) which includes a metal surface operating as a circuit ground layer. The antenna has an end connected through the feeder and the through hole to the metal surface. Outer case 4 is usually made of a nonmetal material such as plastics or resin, and houses therein printed-circuit board 3 and feeder 2. Outer case 4 also supports thereon a display unit comprising liquid-crystal screen 8 and a control unit such as keypad 9. The display unit and the control unit are normally mounted on outer case 4 remotely from feeder 2.
When the cellular phone is used with the antenna assembly extended, the whip antenna is connected to the feeder. When the cellular phone is used with the antenna assembly retracted in the case, the helical antenna (not shown in detailed structure) mounted on the distal end of the whip antenna is connected to the feeder while remaining seated on an upper surface of the outer case. The whip antenna or the helical antenna operates as a transmission antenna dependent on whether the antenna assembly is extended or retracted. The feeder has an end connected to the metal surface as the board ground layer regardless of whether the antenna assembly is extended or retracted. Therefore, a current flows in reality to the metal surface, which operates as an auxiliary antenna. On the cellular phone, the antenna assembly and the metal surface (ground layer) operate as a radiation source for radiating radio waves.
When the user communicates with another party using the cellular phone (an event hereinafter referred to as “call”), the antenna gain and the radiation efficiency are lowered due to the effect of the human body of the user, resulting in a reduction in the communication quality.
A cellular phone according to the invention disclosed in Japanese laid-open patent publication No. 2000-323921 is shown in FIGS. 2(a) and 2(b) of the accompanying drawings. FIG. 2(a) is a cross-sectional view of the cellular phone with an antenna assembly extended, and FIG. 2(b) a cross-sectional view of the cellular phone with the antenna assembly retracted in the case. Reference characters shown in FIGS. 2(a) and 2(b) are identical to those shown in FIGS. 1(a) through 1(c). The cellular phone includes plate 5 made of a magnetic material (hereinafter referred to as “magnetic plate”) inserted in the outer case of the conventional cellular phone. The magnetic plate reflects a radio wave radiated from the antenna into a space where no human body is positioned, with the result that the radio wave is intensified in the space during the call for improved radiation efficiency. The magnetic plate that is used should preferably be minimally capable of absorbing electric power by itself from the standpoint of improving radiation efficiency. It is preferable that the loss term of the complex permeability of the magnetic plate be minimum.
As shown in FIGS. 2(a) and 2(b), magnetic plate 5 which has heretofore been known is positioned on the keypad side in the vicinity of the antenna feeder, and placed in a gap between the printed-circuit board and the outer case.
The incorporation of the magnetic plate into actual cellular phones will be considered below. If a cellular phone has a relatively large thickness, then no particular problem arises in inserting the magnetic plate into the cellular phone as a sufficient gap is provided in the cellular phone.
However, such a gap in a low-profile cellular phone is often filled up with circuit components and display components such as a liquid-crystal panel. For placing the magnetic plate in the low-profile cellular phone, awkward structures (not shown) such as attachments and mechanisms for fixing the magnetic plate in position need to be provided in the gap. For fixing the magnetic plate in position, such attachments are required to be strong enough to withstand certain external forces that will be exerted when the cellular phone is carried around, and hence take up an unexpectedly large space. Therefore, the magnetic plate and its fixing jigs have been responsible for preventing the cellular phone from having a low profile.
It is an object of the present invention to provide a low-profile cellular phone which has improved radiation efficiency, achieved by a magnetic plate, during a call for higher communication quality, and which is of a structure allowing the cellular phone to be of a lower profile than heretofore with the magnetic plate and awkward structures such as its fixing jigs being not disposed in a gap within an outer case of the cellular phone. It is also an object of the present invention to provide a cellular phone having a magnetic plate which is made more effective than heretofore.